So for the first looks... the Android Marshmallow has a good smooth interface.

Both Sims are working and data works on both Sims as well

Unlike Lollipop the Dialer has no lag whatsoever. You can see it in the video for the network settings bug. The dialer is very smooth.

Tempratures are a little uncontrolled while using heavy Apps Chrome etc.
With only messenger usage the tempratures seemed to be well under control

A Brilliant thing I noticed was the Screen wake on notification is black and white and gives a very elegant look to the phone. I tried capturing it using another phone, but the feel in Real is not the same as in the Picture.

Credits for the Video @AndroidFuchs , @sudd1976 , @ghanshyamshinde
Since the operating system is very new, there are apps that do not work properly or do not work at all.

Camera:
The camera is good.
for Comparison these are the photos of the same thing taken during night time to check on the clarity and flash strength etc.
One of the pictures is taken on the MIUI v5 Camera app and the other one is taken on the stock CM13 camera app.
Lets see if you can find which is which!

Well let me disclose it for you.
The one on the left is the one from MIUI v5 Camera app and the one on the right is from the Stock CM13 camera.
I've attached the pics in zip format for you guys to look into the details.

Music:
The Music app has some UI advances from the CM12.1 (the last one I used was long back, so i guess these UI changes have been incorporated in Cm12.1 as well)
The sound clarity is great on the Apple earpods.
Playing Lossless music with Hip Hop as the equalizer setting with Full Bass Boost, and guess what?? There no cracking of sound on the headphones.

But just like in MIUI the Volume Buttons on the Apple earpods don't work.
What works is Double Click on the button for next track, Triple Click for Previous Track, Single Click for Pause and Play.

Antutu Benchmarks:
Running the Antutu Benchmark App
What i noticed was the FPS for a 1280x720 3D rendering ranged from 1.8fps to 12 fps depending on the detail level of the scene
The Final Score is 21k+ (Screenshot attached)

The Google Play Store interface looks different as well

RAM:
The Free RAM with No Apps Installed
With General Google Apps and some Messengers installed

Battery:
Now for Battery Life
Phone Fully Charged at 3:22 PM

At 9:28 PM the Battery use is as follows (Considering 2.5 Hours the Phone was without network on the Primary SIM, But apart from that 3G was ON Fulltime)

At 11:54 after using the phone continously for making the review videos and checking it out
I get close to 2 hours of Screen ON time for a battery drain of 52%.
Extrapolating based on these stats I can say that this ROM would give close to 4 Hours SOT, which is impressive.

Now for something that we have all been looking out for The Doze Mode!

What is Doze Mode?According to a post on androidcentral

You won't have to do anything to use the new Doze feature. There are no switches or settings you need to toggle, and once you've updated to Marshmallow it just works. That is, when it's supposed to work.

And that's the thing. You won't see any benefit from Doze while your phone is in your pocket and you're working or at school. Things need to be idle, and that means really idle.

For Doze to kick in, your phone needs to be sitting still with the screen off, and not connected to a charger. That means no moving around and nudging the gyro or other motion sensors, no touching the screen or the buttons and no waving your hand around in front of it if you're using a phone like the new phones from Motorola that have motion detection on the front bezel. Set it down, and leave it alone.

So to test this.. I charged my phone completely (Screenshot below) and then just let it be on WiFi

I went to sleep
Now since there no indication whatsoever for the doze mode.
All there is to decipher its usefullness is the battery that you wake up with in the morning
So heres the screenshot for the battery use overnight without the phone being touched.

If you see for a 2000mAh battery if the graph shows that the battery will last 2 days on wifi.. its commendable! Right?
But if u see the time for which the doze mode was on, its around 15 mins less than 5 hours or so. So waking up to 88% battery seems to be fairly decent.

Please let me know what happens to your phones in the same situation on MIUI. It would be interesting to understand where MIUI stands on this feautre. Personally I fell MIUI is not far behind.
There will be a difference but I feel it should be only marginal.

System Tuner:

A Feature that is added to CM13 is the System Tuner.
For those using MIUI this feature would not be something out of the blue for you.
To enable this, Long press on the Settings button in the notification shade
Now got Settings and scroll all the way down to find System Tuner

Upon entering theres a notice displayed

Inside you will find

The quick settings is basically the Toggles that are visible on the toggle page (two finger swipe down)
and the Status bar settings encapsulates the icons that will be visible on the status bar.

Another Interesting Feature that I noticed was under Developer Options

The USB Configuration setting now has 3 More options.
Tried using Audio Source, but I think it will work only with USB Speakers or a USB Device that can be a Audio Sink
Haven't tried MIDI or RNDIS. Will update on this later

Bugs Noticed So Far:1. Cannot Change Mobile Network Settings and Cannot Switch from 3G mode on First sim to 2G

2. Going into Battery Light Setting makes it Crash

3. Going into the App Notifications Settings makes it Crash

4. Cannot Apply CM12 themes on CM13. System UI Crashes

5. Text Overlap with center clock when too many toggles are ON

5. The OPtion to integrate the text inside the battery symbol when charging doesn't work

Verdict:-

Good For Regular Use: If you generally stay in places where 3G coverage is there then you should have no problems, otherwise a work around is that you switch the sim card, on which you expect calls and sms, onto the second sim slot.

Smooth and Minimal Lag on Heavy Applications

UI Similar to Lollipop but less laggy.

So This wraps up my review.. I'll keep adding stuff as I come across it!!Hope this review gives you a clean insight of the CM13 features for a regular Daily use.

Great review! I'm glad they fixed the buggy CM12.1 and I hope an official one comes out to check out on my Galaxy.

Please let me know what happens to your phones in the same situation on MIUI. It would be interesting to understand where MIUI stands on this feautre. Personally I fell MIUI is not far behind.
There will be a difference but I feel it should be only marginal.

MIUI is definitely not far behind since it is far ahead. When sleeping with the fully charged phone on wifi I lose 0% battery. Compared to any loss of battery when the phone isn't being used and MIUI is the winner. Losing 12% overnight is pretty standard for smartphones so I'm glad it isn't as bad as lollipop was when you could wake up to 30% or more battery loss. (I had a friend that woke up to a dead phone once lol. It turned out his CM12.1 decided to pretend the charger wasn't plugged in and drained the whole night)

The sad part is that was with Doze on? Now I really want to know what MIUI does that saves battery so well. I know Marshmallow eats up more RAM than Kitkat or earlier versions but that shouldn't do that much to the battery. Since I lose about 10-12% on my old Galaxy S3 phone back on Jelly Bean and that was well before Doze came out I just wonder what Marshmallow is doing in the background that it still lose 12% with the new Doze feature on. How much would it lose with it off?

I thought Doze might have been the same thing MIUI did that saves up on battery as much as it does but I guess Google still has work to do.